Weld-splash shield



y 3 L. E. MITCHELL 2,086,935

WELD SPLASH SHIELD Filed Nov. 21, 1935 INVENTOR LORIS E. MITCHELL WfuATTORNEY Patented July 13,

WELD-SPLASH SHIELD Loris E. Mitchell, Bloomfield, IN. 1., assignor, bymesne assignments, to Radio Corporation of America, New York, N. Y., acorporation of Delaware Application November 21, 1935, Serial No. 50,832

3 Claims.

My invention relates to electric welding, particularly to resistancewelding of metal and to the prevention of splashing of molten metalduring heating.

To join two metal pieces by resistance welding, the faces of the twopieces are placed together and sufficient current passed between the twopieces to heat and fuse them together. To increase the resistance of thecontacting surfaces, a raised bead or boss may be formed upon one memberto provide a line contact between the two members. The relatively smallmass of the raised portion or boss quickly melts away however, and opencircuitsthe two members unless sufficient mechanical pressure is appliedbetween the two members to force them together as the boss softens andmelts. Unfortunately, the relatively high mechanical pressures necessarybetween the members tend to extrude molten metal from between the twofaces of the mem- ,bers and to splash nearby objects, leaving the weldedseam rough in appearance and non-fum form in depth. In welding the partsof a metal envelope of electron discharge devices, molten metal is oftensplashed or sprayed upon the electrodes within the envelope causingshort cir cuits, leakage paths, etc.

It is an object of this invention to prevent the splashing of moltenmetal from a welded seam, and to produce a stronger and more uniformseam.

It is a further object of my invention to improve the manufacture ofwelded metal envelopes of electron dischargedevices.

The desired results, according to this invention, are accomplished byproviding the surfaces to be welded with two or more line contactingpaths, the first of which may be a raised bead or boss formed centrallyalong the surface to be welded. A second contacting path is providedparallel to the first and on the side of the first from which splashingis to be shielded. The passage of sufficient current through the secondmentioned path to soften the metal of the raised portion is prevented byso constructing the second mentioned contacting path that its resistancewill shunt the greater portion of the welding current through the firstmentioned contacting path.

The novel features which I believe to be characteristic of my inventionare set forth with particularity in the appended claims, but theinvention itself will best be understood by reference to the followingdescription taken in connection with the accompanying drawing in whichFigure 1 shows one form of my invention embodying the basiccharacteristics thereof; Figure 2 shows a second basic embodiment of myinvention; Figure 3 shows the essential characteristics of my inventionemployed in the fabrication of a metal envelope, and Figure 4 shows myinvention in modification applied to the metal envelope of a dischargedevice.

The essential characteristics of my invention may be advantageouslyemployed in welding ;o gether two metal plate members. In Figure l, forexample, where the edge of member I is to be joined to the surface ofmember 2, two bosses or raised portions 3 and i are formed along thesurface of member 2. Bosses 3 and 4 which may be pressed, machined, castor rolled on member 2 thus provide two parallel contacting paths betweenthe members i and 2. If, for example, it is desired that molten metal beprevented from splashing to the right, boss must be prevented frombecoming molten during the welding operation by increasing its contactresistance with member i so that a substantial portion of the weldingcurrent will be shunted through boss 3, to localize the molten metal tothe region of boss 3. The resistance between member I and boss l may bemade greater than the resistance between member l and boss 3, forexample, by bringing the lower corner of member l into slidingengagementwith the side of boss 4 and by bringing the face of member I!into direct pressure contact with boss 3. Or, boss 4 may be coated withan insulating material, such as a ferrous oxide, to increase its contactresistance with member 9. With member l forced under mechanical pressuretoward member 2 and upon the application of a welding voltage betweenthe two members, boss 3 first softens and then fuses with the face ofmember l, boss 4 effectively sealing the right hand edge of the seamagainst splashing of extruded metal.

The parallel contacting paths between members I and 2 may, if desired,be formed as shown in Figure 2, where conjugate bosses 3 and 5 upon themembers i and 2 may be formed to provide the two contacting paths. Assuggested in connection with Figure l, the contact resistance of oneboss may be greater than the other, to confine the molten metal of theseam.

The essential characteristics of my invention may advantageously beemployed in the fabrication of metal envelopes for electron dischargedevices. To this end it has been found that one of the two contactingpaths may be formed by means of a third metallic member held in firmcontact with the two members to be welded, this third member-or shieldbeing positioned over the seam to be welded to shield the molten metalagainst extrusion.

The usual metal envelope, Figure 3, of receiving tubes may comprise acup-like shell, 6, with a flanged rim, 1, at its open end. Closure meansfor the shell is a circular disc or header 8 in which have been sealedgas-tight lead-in wires 8 and upon which may be mounted any desiredelectrode arrangement. The rim of the shell is positioned concentricallyupon the header and in registry with a raised head or boss i0 formed inthe face of the header. A cylindrical shaped welding electrode II withan inside diameter slightly greater than the outside diameter of theshell 6 may be. fitted over the shell with the annular face i2 of theelectrode adapted to bear against the radially extending rim 1. Acooperating welding electrode II engaging the lower face of the headerserves with the upper electrode to tightly compress the rim 1 of theshell into engagement with the boss iii.

In the application of my invention to the welding of metal shells todiscs, a thin metal ring I3 is fltted into the end of the shell, withits outer edge extending slightly beyond the plane of the rim' to engagethe face of the disc in a circular line of contact. The outer edge ofthe ring may be crimped or rolled into a V-shaped section I4 so that thering will fold at the apex of the V as the disc is forced against theshell to maintain a uniform and snug engagement between the edge of thering and the disc along the annular line of contact. When the shell andheader are pressed together under the driving force of the weldingelectrodes, the ring folds along the V section and effectively seals theinner edge of the weld seam against inward splashing or extrusion 0 ofmolten metal from within the seam as the boss is melted by the heatingcurrent passed therethrough. 1

The characteristic features of my invention may also be employed assuggested in Figure 4. 5 Here the ring i5 is of uniform diameterthroughout its length and fits snugly in the end of the shell. Upon thecompression of the header 8 against the rim 1 of the shell, the ring l5telescopes inwardly maintaining a uniform and flrm 0 contact along itsouter edge against the face of the header. This construction as inFigure 1,

eilfectively shields the interior of the envelope from splashing moltenmetal from within the seam.

It will be noted that the essential characteristics of my invention maybeemployed in the manbetween the heater and shell have been obtained bypassing a current of the order of 50,000 amperes laterally through theseam for about $5 of a second.

To those skilled in the art many modifications may become apparent in myinvention without departing from the scope thereof. It is accordinglydesired that my invention be limited only by the prior art and by theappended claims.

I claim:

'1. An envelope for an electron discharge device comprising a tubularshell with a radial flange at the rim of one end, a closure disc forsaid end, and a metal ring in annular engagement with the inner wall ofsaid shell and extending axially beyond said flange of the rim and intocontact with said disc.

2. An envelope for an electron discharge device comprising a tubularshell with a radial flange at the rim of one end, a closure disc forsaid end, and a cylindrical metal ring of adiameter equal to theinternal diameter of the tubular shell fltted in said shell with theedge of said ring extending axially outward from the rim of said shelland arranged to telescope slidably inward upon the compression of saidclosure disc over said flange.

3. An envelope for an electron discharge device comprising a tubularshell with a radial flange at the rim of one end, a closure disc forsaid end, and a metal ring in annular engagement with the inner wall ofsaid'shell and extending axially beyond said rim and into contact withsaid disc, the axially extending portion of said ring being V-shaped incross-section.

- LORIS E. MITCHELL.

